1. Field of the Invention
The present invention generally relates to vehicle steering apparatuses and, more particularly, to a steering apparatus of a vehicle suitable for detecting an absolute angle of a steering shaft by using a sensor located near the steering shaft of the vehicle.
2. Description of the Related Art
Conventionally, there is known, as disclosed in Japanese Laid-Open Patent Application No. 2001-194251, a steering apparatus for vehicles which detects an absolute angle of a steering shaft of a vehicle. The steering apparatus comprises a pair of resolver sensors provided to the steering shaft and a multi-rotation absolute detector provided to the steering shaft. The steering apparatus detects an angular position of the steering shaft within a 360°-rotation based on a relationship between output signals of the pair of resolver sensors, and also detects a rotational speed of the steering shaft by using the multi-rotation absolute detector. Therefore, according to the above-mentioned conventional steering apparatus, an absolute angle between a locked position and a locked position of the steering shaft based on the angular position and the rotational speed within a 360°-rotation.
However, in the above-mentioned conventional steering apparatus, since it is necessary to provide the multi-rotation absolute detector to the steering shaft separately from the resolver sensors so as to detect an absolute angle of the steering shaft, a manufacturing cost is increased and a loading space is excessive.
In consideration of this point, it is possible to always detect an angular position of a steering shaft by continuing operations of the resolver sensors and a processing circuit which processes the output signals of the resolver sensors so as to detect an absolute angle of the steering shaft after the ignition key of the vehicle is set to OFF and is pulled out of the keyhole. However, according to such a technique, since an angular position is continuously detected after the ignition key is set to OFF and pulled out of the keyhole, a dark current is increased, which results in a situation where a vehicle battery voltage remarkably drops.